A device of this kind is known from European Patent Application 21534. Because the transducer comprises separate transducer layers for transmission and reception, each of these layers can be optimally adapted to its function. However, it has been found that the transmitter and receiver circuits which are interconnected via the transducer can adversely interfere with one another.
It is an object of the invention to reduce such interference substantially, to uncouple the ultrasonic transmitter and receiver circuits in a suitable manner and, at the same time, to enable control of the sensitivity and attenuation of the transducer.